Eukaryotc Transcription真核转录.pptVIP

Eukaryotic Transcription Eukaryotic Transcriptional Transcription control is the most important mode of control in eukaryotes. Three RNA polymerases: RNA Polymerase I: synthesis of pre-rRNA, which is processed into 28S, 5.8S, and 18S rRNAs RNA polymerase III: synthesis of tRNA, 18 S rRNA, and small, stable RNAs RNA polymerase II: synthesis of mRNAs and four small nuclear RNAs that take part in RNA splicing Eukaryotic Transcriptional The main purpose is the execution of precise developmental decisions (irreversible). Cis-acting control elements are located many kb away from the start site. Promoter region is poorly characterized. TATA box Initiator Instead of a TATA box, some eukaryotic gene contain an alternative promoter element, called an initiator. Initiator is highly degenerative. CpG island Genes coding for intermediary metabolism are transcribed at low rates, and do not contain a TATA box or initiator. Most genes of this type contain a CG-rich stretch of 20-50 nt within ~100 bp upstream of the start site region. A transcription factor called SP1 recognizes these CG-rich region. Gives multiple alternative mRNA start sites. Enhancers Located several Kb away from the start site. Usually ~100-200 bp long, containing multiple 8- to 20-bp control elements. Cell-type specific Direction-less (invertible) Promoter Proximal Elements Occur within ~200 bp of the start site. Contain up to ~20 bp. Cell-type specific Invertible A hypothetic mammalian promoter region A hypothetic yeast promoter region mRNA processing Cleavage and polyadenylation * About 25-35 bp upstream of the start site TATAAA -34 to -26 +1 mRNA start 5’ Well-defined transcription start 5’ Y Y A N T/A Y Y Y +1 Y = pyrimidine (C or T) N = any mRNA Multiple 5’-start sites CpG island ~100 bp +1 Enhancer Enhancer +1 Promoter Proximal element TATA +1 Promoter Proximal Element Enhancer Enhancer Enhancer Intron Exon -30 -200 +10~50 Kb -10~-50 Kb TATA +1 Enhancer ~-90 Exon Intron Poly (A) site 5’ Cap